Is there a formula to figure fan RPMs at different voltages

[grimlykindo]

I just got a few of the rare Yate Loon D12SM-12 Blue LED fans for my P180. I already have all Nexus fans, but 1000RPM limit isn't enough for my cooling setup, so I got these cause they run 1650 RPM @ 12Volts. Insted of the 1000RPM @12Volts like the Nexus fans. They are great fans and run very quiet when softmounted.

Link here- http://www.case-mod.com/store/120mm-cas...2-sensitive-with-blue-leds-p-1708.html

I currently am using a Sunbeam Rheobus to control my fans. Currently I have the Yate Loons running right around 7Volts and they seem to move a decent more amount or air at 7 volts then my Nexus did at 12 Volts. But I'm wondering what RPMs are my Yate Loons doing at 7 Volts? I want to compare these fans, but I would really like to know the RPMs

There must be some kind of formula to figure this out. Anybody out there know?

 

[Cheetah8799]

I don't know of any general formula because each fan has a different motor in it. nothing is really standard. So while one fan does X rpm at 7v, another fan of seemingly same size and shape but different manufacturer will do Y rpm at 7v. know what I mean?

 

[suszterpatt]

Can't you just hook it up to your mobo and use SpeedFan to check? Or does it have no RPM monitoring?

 

[grimlykindo]

Originally posted by: Cheetah8799
I don't know of any general formula because each fan has a different motor in it. nothing is really standard. So while one fan does X rpm at 7v, another fan of seemingly same size and shape but different manufacturer will do Y rpm at 7v. know what I mean?

Yeah, I see what you mean. I know that its not a direct correlation between numbers - I mean I can phisically tell that at 7v the Yate Loon is pushing more air than the Nexus @ 12. But if the numbers were directly correlated that would mean that 7v is just over 1/2 the power of 12v. That would mean that at 7v it would be running 1650RPM x 7/12(volts) which equals 962 RPMS. That cannot be right!

So I guess that your right, there is no formula or correlation between the RPMs and volts unless comparing identical fans (but even then there could be manufacturing inperfections)

 

[grimlykindo]

Originally posted by: suszterpatt
Can't you just hook it up to your mobo and use SpeedFan to check? Or does it have no RPM monitoring?

Yes, but its running through a Sunbeam Rheabus. How would I plug it into the mobo and the Rheabus? If I power it through the mobo it will go to its original 12v and if I use speedfan to turn it down there is no way to tell when its at 7v. (with the Rheabus the LEDs change colors when you pass 7v)

 

[RampantAndroid]

Get a 3 pin splitter that takes the red & black to the fan speed controller, and the yellow (moniter) wire to the mobo fan connection. This will allow your mobo to see the RPMs, while you still control the speed.

This sort of implementarion was used in the thermaltake Volcano 7...this thermaltake uses the same setup: linky

There is no equation though, each motor is different....diffeent windings and control circuits. If you got into physics II stuff and knew the strength of the permanent magnets, the number of windings and gauge, yeah you COULD get an equation....

 

[Zepper]

All you have to do is remove the contact on the end of your yellow wire from the 3-pin connector, get another 3-pin female shell, and put the contact from the yellow wire in that. You can then get power from the Rheobus and still read the rpms from the mobo connector. Ground is common on PCs so you generally don't need the black wire to go to the mobo connector but sometimes there is noise that can mess with the tach reading. So you could wrap a black wire around the yellow and connect it at the mobo connector (will need a crimp-on contact for the black wire - jab-tech.com, svc.com, etc. sell 3-pin contacts and shells). The black wire would act as a shield for the yellow wire.

.bh.

 

[grimlykindo]

Originally posted by: Zepper
All you have to do is remove the contact on the end of your yellow wire from the 3-pin connector, get another 3-pin female shell, and put the contact from the yellow wire in that. You can then get power from the Rheobus and still read the rpms from the mobo connector. Ground is common on PCs so you generally don't need the black wire to go to the mobo connector but sometimes there is noise that can mess with the tach reading. So you could wrap a black wire around the yellow and connect it at the mobo connector (will need a crimp-on contact for the black wire - jab-tech.com, svc.com, etc. sell 3-pin contacts and shells). The black wire would act as a shield for the yellow wire.

.bh.

Thanks Zepper, I would have never thought of that. I actually think I have a spare 3-pin connector I can use. I'm pretty sure I don't need a ground - My old PC had 4-pin fans with a yellow wire coming out separaty to monitor RPMs and it worked fine

I might even make a splitter/adapter thing so I can test a buch of fans I have at different voltages without moding each fan's wires. It would just be a 3-pin female going to two 3-pin male plugs (one with black/red, and one with the yellow RPM wire.

Thank for the idea Zepper!

 

[Jeff7]

Just don't hook the RPM wire to the wrong motherboard pin. Might wind up frying the fan's circuitry, or worse, damage the motherboard should it short out the fan header.